Non-invasive neuro-cranial stimulation is an application of current through one or more electrodes on the neck or head for the purpose of changing function of nervous system. The purpose may be therapeutic including the treatment of neuropsychiatric diseases, epilepsy, depression, Parkinson's disease, Alzheimer's Disease, neuro-degenerative disorders, obesity, and Obsessive-Compulsive-Disorder. The purpose may also be to enhance or accelerate cognitive performance, learning, or perception related tasks.
Non-invasive neuro-cranial stimulation (NINCS) inherently involves passing current through an electrode into or across the skin. Transcranial direct current stimulation (tDCS) is an example of non-invasive neurocranial stimulation in which direct current is applied directly to the scalp in order to pass current to specific brain regions. NINCS can lead to a wide range of discomfort in the subject receiving electrical stimulation. Discomfort can include any perception of tingling, pain, burning, or an otherwise undesirable sensation. Additionally, skin irritation may occur, with such manifestations as flaking, redness, inflammation, burns, or any change in skin properties. Discomfort and irritation may occur together or separately. They typically occur just under or around the electrode, but may occur between electrodes or elsewhere. Discomfort is typically experienced during or immediately after stimulation, but may be felt at longer time points after stimulation has been ceased. Irritation is most pronounced during or right after stimulation, but may be manifested a while after stimulation.
Irritation and discomfort are not desired during NINCS for several reasons. Irritation and discomfort cause pain or discomfort to the subject, complicate the desired effect of stimulation, and can lead to adverse health effects. Further, irritation and discomfort may prevent optimal application of NINCS and reduce a subject's desire to receive NINCS.
Conventional tDCS (a type of NINCS) employs the passage of a constant direct current (nominally 260 uA-3 mA) between an anode and cathode electrode, at least one of which is placed over the scalp. The spatial focality (targeting) of tDCS is considered pivotal for efficacy and safety. Decreasing electrode scalp contact area is considered to improve spatial focality. But for a given electrode current, reducing contact area increases current density, which in turn may increase hazards.
From the perspective of tDCS safety, it is important to consider 1) injurious effects of electrical currents on the brain; and 2) pruritic, painful, or injurious effects of electrical currents on the skin. Brain injury and skin effects are not necessarily linked, and therefore should be considered independently. For example, stimulation causing skin irritation may not have any adverse effect on brain function, and brain injury may not be concomitant with skin irritation.
The prior art electrodes fail to address minimizing skin irritation and pain during electro-stimulation activities like NINCS, particularly tDCS. It is an object of the invention to optimize electrode parameters to minimize skin irritation and pain, with a specific focus on engineering small, more focal electrodes.